The present invention relates to expansion joints for flue systems and ducting and pertains particularly to improved non-metallic expansion joint for providing stress relief in refractory lined flue and ducting systems for high temperature applications such as power plants.
In power generating or cogeneration plants, including facilities for obtaining useable electrical power or processing steam/hot water from the burning of solid, liquid or gaseous fuel products, particulate matter such as sorbents and unburnt fuel is recirculated through the combustion. Hot flue gases generated by the combustion process are laden with ash and other particulate matters and are typically directed through a series of processing areas to remove particulates and environmentally hazardous components before finally being exhausted from the facility. FIG. 1 illustrates a power generation plant of unique design that includes a furnace having a circulating fluidized bed (CFB) wherein various fuel materials are combusted. The hot flue gases containing combustion by-products are transferred from the furnace through a flue duct/expansion joint to a cyclone separator.
The cyclone separator diverts heavier combustion particulate such as sorbents and unburnt fuel matter back to the CFB, through a loop seal assembly, which lifts the heavy particulates, mixes them with freshly fed fuel, and introduces the mixture to the combustion chamber. The fine particulate matter and hot flue gases are directed through a heat exchanger. The fine particulate matter is then diverted to a particulate filter for disposal. Gases emitted from the facility will have most of the combustion by-product emissions, including NO.sub.x, SO.sub.2, CO, particulates, etc., removed therefrom, resulting in an environmentally safe means of power generation.
Nonmetallic expansion joints are flexible connectors designed to provide stress relief in flue duct systems by absorbing differential movement caused by thermal changes. They also act as vibration isolators, and in some instances, make up for minor misalignment of adjoining flue ducts and/or equipment. They may be fabricated from a wide variety of nonmetallic materials, including synthetic elastomers, fabrics, insulation materials and other suitable materials depending upon the designs thereof. Since their introduction in the early 1960's, the use of nonmetallic expansion joints has continuously grown.
The advent of more rigid emission standards has caused the use of more complex flue work systems. Nonmetallic expansion joints have been used in place of the traditional all metal expansion joints to solve problems caused by the thermal and mechanical stresses generated in these complex systems. Although the major user of the nonmetallic joint continues to be the power generation industry, the use of this product has expanded into many other industries wherein gases are conveyed including pulp and paper plants, refineries, steel mills, foundries, smelters, cement plants, kilns, refuse incineration, marine applications, vapor-heat-dust recovery, food processing, and HVAC (Heating, Ventilating and Air Conditioning).
A typical prior art nonmetallic expansion joint is shown in FIG. 2. The joint includes a pair of angle brackets mounted to the respective ends of a pair of adjoining ducts or flues. A pair of frame members are in turn attached to the angle brackets. The frame members have mounted thereto a flexible pressure seal that extends around the periphery of the expansion joint. The pressure seal may be of the elastomeric type for operation below 400.degree. F. or may be of the composite type for operation at temperatures continuously above 400.degree. F. It will be appreciated that the flexible pressure seal allows relative axial, transverse, angular and rotational movement between the respective ducts while preventing the escape of pressurized flue gases and particulates carried therein. Other nonmetallic expansion joint constructions may be seen in the "Technical Handbook" published by the Ducting Systems Nonmetallic Expansion Joint Division of the Fluid Sealing Association, 2017 Walnut Street, Philadelphia, Pa. 19103 (2nd Edition), the contents of which are fully incorporated herein by this reference.
It is known that nonmetallic expansion joints are prone to failure from the build-up of abrasive particulates carried by the flue gas stream, which can accumulate in the expansion joint in such quantities that they eventually rupture the pressure seal. Moreover, fly ash and other particulates can cause damage to the expansion joint by solidifying to a cementatious state. Also, certain non-cementatious particulates (fly ash) can create a sever, corrosive (acidic) environment when subjected to cooling (below the H.sub.2 SO.sub.4 dew point) during a maintenance outage.
To prevent premature expansion joint failure from the build up of particulate matter therein, baffles have been proposed to help direct particulate matter beyond the expansion joint, as shown in FIG. 2. Other proposals include mounting the flexible pressure seal substantially flush with the interior surface of the duct or flue, as shown in FIG. 3, or mounting an insulation barrier behind a baffle arrangement as shown in FIG. 4. Although these proposals may exhibit varying degrees of effectiveness in minimizing expansion joint failure, the arrangement of FIG. 3 may result in thermal transfer on the inner face of the expansion joint and abrasion from particulates in the gas stream. A greater setback would be desirable. The arrangement of FIG. 4 may result in the insulation barrier rubbing on the baffle under negative pressures. Moreover, the insulation barrier must be fixedly attached to both sides of the joint, which may complicate joint construction and also impart adverse loads on the barrier.
To overcome the problems of the prior art, we have developed improved loop seal expansion joint assemblies as set forth in the aforementioned parent applications. While these improvements have gone a long way toward solving many of the problems, they have not all been solved. In spite of the improved seal construction, cyclone inlet and outlet expansion joints fill up with ash and prevent proper movement. Differing expansion rates between combustion outlets, connection cage inlets and the cyclone result in large face to face movement and axial movement of the expansion joints.
Accordingly, there is an evident need for an expansion joint flexible seal assembly which not only prevents particulate build up, but which is durable, easy to install and will perform satisfactorily despite joint movement. It would be further desirable to provide an expansion joint flexible seal assembly that also performs a deflection function to provide an additional sealing barrier to the entry of ash into the seal.
The present invention accomplishes the foregoing objects and advantages. It is therefore an object of the present invention to provide an improved expansion joint seal and flexible shield therefor.
It is a further object of the present invention to provide an expansion joint having a flexible shield that is not adversely affected by relative joint movement.
It is a further object of the present invention to provide an expansion joint having a modular construction for easier installation.